Investigators say they believe they know the identity of the attacker, and that he is thought to have acted alone but was “inspired by international terrorism”.

The House of Commons will sit this morning, with prime ministerTheresa May saying the country would not be cowed:

Parliament will meet as normal. We will come together as normal.

And Londoners – and others from around the world who have come here to visit this great city – will get up and go about their day as normal.

They will board their trains, they will leave their hotels, they will walk these streets, they will live their lives. And we will all move forward together. Never giving in to terror. And never allowing the voices of hate and evil to drive us apart.

London is the greatest city in the world and we stand together in the face of those who seek to harm us and destroy our way of life.

UK foreign minister Boris Johnson, who is in the US for an international meeting discussing the Isis threat, said:

Heartbreaking. This is not the first attack on London or our Parliament - and won’t be the last - but our values will prevail.

The terror threat level for the UK remains unchanged, at “severe”. The Metropolitan police said extra patrols, armed and unarmed, would be in place, “particularly in crowded places and iconic locations”.

The Queen has postponed a planned visit to Scotland Yard that was due to take place today.

A terrorist attack has occurred in the United Kingdom. I offer my deepest condolences to the victims and extend my sympathy to all those who were wounded.

Terrorism is absolutely intolerable. Japan stands in solidarity with Prime Minister May of the United Kingdom, as well as with its people during this difficult time.

Prime Minister May has conveyed the message that the United Kingdom is firm in the fight against terrorism. Japan offers its full support to Prime Minister May and will combat terrorism in cooperation with the international community.

Wall Street Journal: London rampage leaves 4 dead

The attack outside the Houses of Parliament in London is the latest in a series of terrorist atrocities involving a vehicle being driven at speed into pedestrians – a tactic actively promoted by Islamic State.

“If you are not able to find a bomb or a bullet, then smash his head with a rock, or slaughter him with a knife, or run him over with your car, or throw him down from a high place, or choke him, or poison him,” he said.

Though al-Adnani, who was killed in 2016, pointed a finger specifically at France, where there were two vehicle attacks in 2014, he also cited the UK among preferred targets.

• This section of the live blog was amended on 23 March 2017 to clarify a reference to the Berlin truck attacker.